Geochemistry of Lower Palaeogene bauxites – unique signature of the tectonostratigraphic evolution of a part of the Croatian Karst

Abstract

Investigation of the origin and emplacement of Istrian Lower Paleogene Bauxites (ILPB) discussed in this work relies on the recent perspectives on development of the collision-induced diachronous discontinuity surface in the Istrian part of the Adriatic-Dinaric Carbonate Platform (ADCP). This process, related to the forebulge uplift at the latest stages of Alpine orogenesis, is amply recorded in the geochemical signature of contemporaneous bauxites. In order to elucidate the patterns of bauxite formation a discriminant function model based on the Compositional Data (CoDa) analysis (major and trace elements) is constructed providing the solid ground for separation of the bauxite groups deposited in the subaerially exposed Istrian palaeoenvironment. Complete distinction between the four a priori defined ILPB groups achieved by the analysis demonstrates the highest degree of efficiency in characterizing environmental conditions marked by the unique suite of geochemical variables (compositions). In the last analysis, the current model characteristic for NW compartment of Adriatic South Western Unit (ASWu) is cross-compared with the analogous model of the entire ADCP borrowed from earlier investigation but reconsidered within the CoDa framework. It is done with the purpose of assessing the geochemical correspondence between the two event-markers (ILPB and LPB) and clarifying the nature of tectonostratigraphic constraints, especially with regard to the forebulge development in parts of the Adriatic-Dinaric Carbonate Platform.  

Keywords

• Bauxite geochemistry
• Compositional Data
• Discriminant function model
• Forebulge
• Adriatic–Dinaric Carbonate Platform
• Croatia